In order to connect two optical cables of the "ribbon type" to each other, that is, cables in which several optical fibers are disposed in parallel to each other and united together by a single plastic coating so as to form a ribbon and one or more ribbons are joined to form the cable, it is necessary to arrange each optical fiber of a ribbon forming one cable in alignment with the corresponding fiber of a ribbon forming the other cable so as to allow light to pass from one fiber to the other while minimizing dispersion and attenuation of the transmitted signal resulting from faults in the fiber alignment.
For the purpose of achieving such alignment simultaneously in all fibers forming the ribbon, the end of the ribbon itself is conveniently fitted into a rigid body, named a "connector", which keeps the fibers in a geometrically definite position. Two connectors forming a pair are, therefore, arranged and held in a confronting relationship and aligned in order to form a connecting means so that the respective fibers can be constrained to the correct position for forming the optical connection.
Due to the requirements for a connection in which the best alignment between all the fibers of the ribbon is achieved so as to limit the attenuation of the light signal to the minimum when passing through the connection, it is necessary to provide very reduced tolerances as regards possible faults in coaxial alignment between the fibers of each interconnected pair and, as a result, very reduced tolerances in the sizes and positions of the housings for the fibers themselves in the connectors. In particular, by way of example, for connecting ribbons made of single-mode fibers in which the diameter .phi. of the cladding of each fiber is 125 micrometers and the mode diameter is equal to 9.5 micrometers, the position fault of the axis of a fiber in a connector with respect to the axis of the corresponding fiber in the facing connector, must not be higher than one micrometer, so that in most cases the signal attenuation at the connection may be lower than 1 dB which is deemed to be the maximum permissible loss value in the connection.
To make connectors meeting these accuracy requirements is quite a delicate operation, taking particularly into account the fact that it is necessary to produce a great number of connectors to be matched while ensuring the same qualitative alignment value for all of them.
For such purpose, connectors are known in which the optical fibers are housed within the grooves of a plate made of crystalline material which are obtained with several steps by localised etching at positions defined by protection templates.
Therefore, in order to achieve the very high accuracy in size required for the housing grooves in a plate, the position and shape of which directly defines the axis position of the fiber contained therein, particularly delicate and expensive working processes are required in producing said plates.
Grooved plates can also be made using a metallic material by cold plastic deformation or coining. Such working ensures a precise reproduction of the features of the punch or die used, and therefore, the achievement of the desired accuracy level is bound to the manufacturing accuracy 25 of the punch itself.
However, common mechanical precision operations, such as grinding, do not ensure the required reduced tolerances while, on the other hand, operations checked by optical instruments and the like, which are adapted to permit size differences smaller than the range of the required precision to be detected, are very expensive if applied to the entire workpiece manufacture.